Fix baremetal arm_compute_validation build errors

* Add -C flag to instruct preprocessor not to strip comments. This is to
prevent marker comments like '// fall through' that suppresses certain
warnings from being removed.

* Fix unused variable warnings.

* Add M_PI definition that's missing from certain toolchain standard
libraries.

Resolves COMPMID-4054

Change-Id: I1d641db668685d4b678f3d0efed84bfe9e630b4b
Signed-off-by: SiCongLi <sicong.li@arm.com>
Reviewed-on: https://review.mlplatform.org/c/ml/ComputeLibrary/+/4692
Reviewed-by: Georgios Pinitas <georgios.pinitas@arm.com>
Comments-Addressed: Arm Jenkins <bsgcomp@arm.com>
Tested-by: Arm Jenkins <bsgcomp@arm.com>
diff --git a/src/core/NEON/kernels/arm_gemm/gemm_quint8.cpp b/src/core/NEON/kernels/arm_gemm/gemm_quint8.cpp
index 84628c0..eead592 100644
--- a/src/core/NEON/kernels/arm_gemm/gemm_quint8.cpp
+++ b/src/core/NEON/kernels/arm_gemm/gemm_quint8.cpp
@@ -69,15 +69,15 @@
 },
 #ifdef SVE2 // Requantizing kernels include some SVE2 only instructions (SQRDMULH, SRSHL)
 {
-    GemmMethod::GEMM_HYBRID, 
+    GemmMethod::GEMM_HYBRID,
     "sve_hybrid_u8qa_dot_4x4VL",
-    [](const GemmArgs &args, const Requantize32 &qp) { return quant_hybrid_asymmetric(qp); },
+    [](const GemmArgs &, const Requantize32 &qp) { return quant_hybrid_asymmetric(qp); },
     nullptr,
     [](const GemmArgs &args, const Requantize32 &qp) { return new GemmHybridIndirect<cls_sve_hybrid_u8qa_dot_4x4VL, uint8_t, uint8_t, Requantize32>(args, qp); }
 },
 #endif
 {
-    GemmMethod::GEMM_HYBRID, 
+    GemmMethod::GEMM_HYBRID,
     "sve_hybrid_u8u32_dot_6x4VL",
     nullptr,
     nullptr,